The Department of Defense (DoD) Tuesday announced that it opened a criminal investigation into the apparent leak of classified documents online in recent weeks. The leaked documents include classified Ukrainian war plans and sensitive materials regarding US allies.

Assistant to the Secretary of Defense for Public Affairs Chris Meagher said, the DoD will “review and assess the veracity of the photographed documents that are circulating on social media sites, and that appear in some cases to contain sensitive and highly classified material.” According to Meagher, the DoD has commenced interaency efforts to assess the impact the leaked documents could have on the national security of the US, as well as the US’s allies and partners.

As a part of the interagency effort, the Department of Justice (DOJ) has launched a criminal investigation as to the source of the leak. As for the DoD, Meagher said, “The Department of Defense’s highest priority is the defense of our nation and our national security.”

The New York Times (NYT) first broke the news of the classified document leak on April 6. The NYT reported that the documents included classified war documents detailing plans from the US and NATO in support of the Ukrainian military ahead of a planned offensive against Russia. Also included in the leak were sensitive materials on several US allies including Canada, Israel and South Korea.

The NYT reported that, according to military analysts, the documents regarding the Russia-Ukraine war seemed to be modified to alter the reported number of deaths both on the Ukrainian side and the Russian side. It also reported that the manner in which the documents ended up on social media was uncertain.